4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

What is a mutation?

Answer 1

An alteration to the DNA base sequence.
Often arise spontaneously during DNA
replication.

Question 2

Why might a mutation not lead to

change in the amino acid sequence?

Answer 2

● Genetic code is degenerate so
mutation may end up coding for same
amino acid as the original triplet.
● Mutation may occur in intron.

Question 3

What is a substitution mutation?

Answer 3

When a nucleotide in the DNA sequence
is replaced by another. This is more
likely to be a quiet mutation, meaning no
change occurs in the amino acid
sequence.
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Question 4

What is a deletion mutation?

Answer 4

When a nucleotide in the DNA sequence
is lost. This is more likely to be harmful
and significant, as it leads to a frame
shift which means the entire amino acid
sequence will be different.

Question 5

What is a mutagenic agent? Give

examples of this.

Answer 5

Factors that increase the rate of gene
mutation. X-rays, UV light, gamma rays,
certain chemicals e.g. in alcohol and
tobacco.

Question 6

What is a polyploidy chromosome

mutation?

Answer 6

Where an individual has three or more

sets of chromosomes instead of two.

Question 7

What is chromosome non-disjunction?

Answer 7

When chromosomes fail to separate
correctly in meiosis, resulting in gametes
with one more or less chromosome than
normal.

Question 8

What is meiosis?

Answer 8

A form of cell division that produces four
genetically different haploid cells (cells
with half the number of chromosomes
found in the parent cell) known as
gametes.
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Question 9

How does meiosis differ from mitosis?

Answer 9

● Meiosis produces four genetically different
cells with half the number of chromosomes
as the parent cells.
● Mitosis produces two genetically identical
cells with the same number of
chromosomes as the parent cells.

Question 10

What happens during meiosis Ⅰ?

Answer 10

1. Homologous chromosomes pair to form bivalents.
2. Crossing over (exchange of sections of genetic
   material) occurs at chiasmata.
3. Cell divides into two. Homologous chromosomes
   separate randomly. Each cell contains either
   maternal or paternal copy.

Question 11

What happens during meiosis Ⅱ?

Answer 11

1. Independent segregation of sister
   chromatids.
2. Each cell divides again, producing 4
   haploid cells.

Question 12

In which two ways does meiosis produce

genetic variation?

Answer 12

1. Crossing over during meiosis Ⅰ
2. Independent assortment (random
   segregation) of homologous
   chromosomes & sister chromatids
   Result in new combinations of alleles

Question 13

Describe the process of crossing over and explain how it increases genetic diversity?

Answer 13

• Homologous pair of chromosomes associate
• chiasmata form
• Equal lengths of non sister chromatids are exchanged
• Producing new combinations of alleles